1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more specifically to a method for manufacturing a semiconductor device using a porous low dielectric constant insulating film.
2. Background Art
In recent years, the speed of semiconductor device has significantly increased, and concurrently, transmission delay due to the lowered signal transmission speed caused by wiring resistance in a multilayer wiring portion, and parasitic capacitance between wirings or between wiring layers has caused problems. Such problems tend to be more significant, because wiring resistance rises and parasitic capacitance increases with the reduction of wiring width and wiring distance accompanying the high integration of semiconductor devices.
Heretofore, in order to prevent signal delay caused by such a rise of wiring resistance and increase of parasitic capacitance, a copper wiring substituting an aluminum wiring has been introduced, and the use of an insulating film having a low dielectric constant (hereafter referred to as low-k film) has been examined as an interlayer insulating film.
One of the methods for forming a copper wiring using a low-k film is the Damascene method. This method has been known as a method for forming a wiring without etching copper, in view of the fact that copper is more difficult to control the etching rate than aluminum.
Specifically, the Damascene method is a method for forming a copper wiring layer, wherein an opening is formed by the dry etching of a low-k film using a resist film as a mask, and then, the resist film is removed by ashing, and a copper layer is embedded in the opening. The copper layer can be embedded by forming a copper film so as to fill the opening using a plating method, and the surface is planarized using a CMP (chemical mechanical polishing) method so as to leave the copper film only in the opening.
On the other hand, as low-k films, organic insulating films, such as an SiOC (carbon doped silicon oxide) film formed by introducing methyl groups into an SiO2 (silicon oxide) film, and a polyarylether derivative film, have been known. However, since the dielectric constant of these films is about 2.6 to 2.9, further reduction of the dielectric constant has been demanded toward semiconductor devices in the generation when further miniaturization of the design rule has been progressed. Therefore, the use of a porous low-k film having pores of a diameter of several to several tens of angstroms has been expected (see, e.g., Japanese Patent Laid-Open No. 2002-50687 and Japanese Patent Laid-Open No. 11-310411 (1999)).
Heretofore, a porous low-k film has been formed by applying a polysiloxane resin composition containing a pore-generating material (porogen) onto a semiconductor substrate, and performing heat treatment to the polysiloxane resin composition.
The heat treatment accelerates the curing reaction of polysiloxane, and simultaneously causes the decomposition and vaporization of the pore-generating material. This results in formation of a lot of micro pores in the insulating film. Here, if the decomposition of the pore-generating material is activated before the completion of the curing reaction of polysiloxane, the size of the generated pores becomes small, and porosity lowers. Therefore, the conventional methods have been designed to activate the decomposition of the pore-generating material at a temperature higher than the curing temperature of polysiloxane. Specifically, in order to generate pores, the polysiloxane resin composition has been heat-treated at a temperature of 400° C. or above.
However, there has been a problem that heat treatment at such a high temperature causes the reliability of copper wirings to lower. Therefore, it is an urgent necessity to develop a heat treatment method that can be performed at a lower temperature.
In the steps of dry etching and ashing in the Damascene method, the porous low-k film is easily undergone charging damage by plasma. Furthermore, in the cleaning step, the cleaning solution easily permeates into the porous low-k film. There has also been a problem that the properties of the porous low-k film as an interlayer insulating film are thereby affected to lower the electrical properties and reliability of the semiconductor device.